Field of the Invention
The present invention relates to the field of starter culture compositions, in particular frozen and freeze-dried starter culture compositions. Moreover, the invention relates to the production of the frozen and freeze-dried starter culture compositions and their use in manufacturing numerous food and feed products.
Description of Related Art
Lactic acid bacteria are used world-wide in the dairy industry to produce a variety of fermented dairy products such as cheese, yoghurts, sour cream, kefir, butter and koumiss. Selected strains of lactic acid bacteria initiating and carrying out the desired fermentations essential in the manufacture of the above products are often referred to as starter cultures.
Lactic acid bacteria commonly used in the food industry can be divided into mesophilic lactic acid bacteria including the genera Lactococcus, Leuconostoc and Pediococcus and thermophilic lactic acid bacteria including the genera Streptococcus and Lactobacillus. While mesophilic lactic acid bacteria have a optimum growth temperature of about 30° C., thermophilic lactic acid bacteria have a optimum growth temperature of about 40° C. to about 45° C.
Starter cultures can be inoculated directly into milk without intermediate transfer and/or propagation. Such starter cultures are generally referred to as direct vat set (DVS) or direct-to-vat inoculation (DVI) cultures.
Starter cultures are generally available from commercial manufacturers in lyophilized/freeze-dried, frozen or liquid form. They can comprise only a single lactic acid bacterium species, but can also be mixed cultures comprising two or more different lactic acid bacterium species.
In order to maintain high cell counts, improved stability and/or viability and/or metabolic activity of lyophilized/freeze-dried, frozen and liquid starter cultures, the addition of additives such as nutrients and cryoprotectants is typically employed.
In EP-0259739-A1 in the name of Miles Laboratories a cryoprotectant together with a combination of citric acid and glucose or a carbohydrate containing glucose linkages are added to culture suspensions before freezing and subsequent freeze-drying of the cultures. The cryoprotectant in EP-0259739-A1 may be sucrose, a peptone, casitone, a salt of glutamic acid, glycerol, dimethyl sulfoxide, non-fat dry milk, casein, whey, fructose or maltose. The combination of citric acid and glucose or the carbohydrate containing glucose linkages acts as a potentiator of the cryoprotectant and further increases the storage stability of the freeze-dried culture concentrate.
WO91/11509 in the name of ICI describes freeze-dried cultures comprising a combination of an ascorbic acid antioxidant and a monocarboxylic α-amino acid which acts as a potentiator for the antioxidant. Said combination is added to the cultures before freezing and subsequent freeze-drying of the cultures. Optionally, a combination of a carbohydrate and a viscosity inducer and a cryoprotectant is added as well. The cryoprotectant may be a glycopeptide and/or the non-toxic, water soluble salt thereof, non-fat skimmed milk powder and/or whey powder, or may be the carbohydrate such as sucrose, mannitol, trehalose, inositol, adonitol and combinations of two or more of these carbohydrates.
WO00/39281 in the name of Chr. Hansen A/S describes a liquid (i.e. a non-frozen) starter culture comprising additives that have a metabolic activity stabilizing effect on the cultures during storage. These liquid starter cultures are presented as a useful alternative to the use of commercial frozen and freeze-dried starter cultures. A suitable additive which, according to WO00/39281, has a metabolic activity stabilizing effect on the cultures during storage is a compound selected from the group consisting of formic acid, a formate, inosinate (IMP), serine and a compound involved in the biosynthesis of nucleic acids, including adenosine-5′-monophosphate (AMP), guanosine-5′-monophosphate (GMP), uranosine-5′-monophosphate (UMP), cytidine-5′-monophosphate (CMP), adenine, guanine, uracil, cytosine, adenosine, guanosine, uridine, cytidine, hypoxanthine, xanthine, hypoxanthine, orotidine, thymidine, inosine and a derivative of any of such compounds.
WO2004/065584 in the name of Chr. Hansen A/S discloses frozen lactic acid bacteria comprising a cryoprotectant agent. The cryoprotectant is added to the bacteria prior to the freezing the bacteria resulting in a homogenous mixture of bacteria and cryoprotectant. The term “a cryoprotective agent” is defined in WO2004/065584 as a substance that is able to improve the storage stability of the frozen culture. The cryoprotective agent in WO2004/065584 may be selected from proteins, protein hydrolysates and amino acids. Preferred suitable examples of these include the ones selected from the group consisting of glutamic acid, lysine, Na-glutamate, Na-caseinate, malt extract, skimmed milk powder, whey powder, yeast extract, gluten, collagen, gelatin, elastin, keratin and albumins. Alternatively the cryoprotective agent may be a carbohydrate. Preferred suitable examples of these include the ones selected from the group consisting pentoses (eg. ribose, xylose), hexoses (eg. fructose, mannose, sorbose), disaccharides (eg. sucrose, trehalose, melibiose, lactulose), oligosaccharides (e.g. raffinose), oligofructoses (e.g. Actilight, fribroloses), polysaccharides (e.g. maltodextrins, xanthan gum, pectin, alginate, microcrystalline cellulose, dextran, PEG), and sugar alcohols (such as sorbitol, mannitol). Also mixtures of cryoprotectants have been disclosed.
WO2005/003327 in the name of Chr. Hansen A/S discloses frozen or freeze-dried cultures comprising one or more cryoprotectants selected from the group consisting of one or more compound(s) involved in the biosynthesis of 5′-nucleic acids or one or more derivative(s) of any such compounds. Inclusion of 3% sodium formate in the frozen lactic acid bacterial culture was found to decrease the storage stability.
WO2005/080548 in the name of Chr. Hansen A/S discloses frozen cultures comprising cryoprotectants. The cryoprotectants are added to the cultures before freezing the cultures.
WO2009/056979 in the name of Danisco discloses frozen starter culture compositions comprising frozen bacteria pellets and separate frozen formate and/or purine pellets and furthermore discloses lyophilized starter culture compositions comprising lyophilized bacteria to which powdered forms of formate and/or purine are added. WO2009/056979 does not disclose the use of a cryoprotectant in the production of the frozen bacterial pellets or the lyophilized bacteria.
In view of the importance of the performance of starter cultures, there is a continuing need in the art to provide starter cultures having improved metabolic activity. The present invention addresses this need.